I can't find any examples, has it just never happened before or is it impossible because of environmental factors?
Apart from the fact that only a few tropical cyclones follow a more southerly route (a list bellow) after going around the North Atlantic, I think the main problem is that tropical cyclones would weaken significantly after landfall in the Iberian Peninsula. An example of this is Hurricane Raphael in 2012. Source Weather.unisys.com.
There is no "easy" path from the Atlantic into the Mediterranean for a system the size of a tropical cyclone. Other examples that followed a similar path but never made it the Mediterranean: Gordon (2006), Jeanne (1998), Ivan (1998), Frances (1992), Bob (1991), Arlene (1987), Chloe (1967), Carol (1965), Dolly (1953).
While the cyclones at the point of approaching the Iberian Peninsula are still tracked as tropical depressions, their characteristics are often similar to other extra-tropical storms.
Mediterranean tropical cyclones are extremely rare but do occur. These are not Atlantic type hurricanes, they are typically not the product of a hot African tropical depression. The most recent event was in November 7, 2014 3.
As for Atlantic basic hurricanes, it would seem nearly impossible. The normal path of the storm leading it eastwards would be affected by the Gulf stream and North Atlantic Drift and would carry the storm north east.
Typical wind patterns along the subtropics also would carry a storm trending east to the North and East.